Effects Of Earthworm Activities On The Population And Community Structure Of Soil Organism In Agro-ecosystem

Earthworms are the most important macro-animal in soil and they play an important role on the substance cycling and the energy flow through modifying soil physical, chemical and biological properties in terrestrial ecosystem. Earthworms directly or in directly influence soil habitation (soil organisms) via their comminution, feeding, burrowing, casting activities and dispersal. However, much of the current studies about the effect of earthworms on the populations of soil microorganism and microfaunal and enzyme activities were concluded from either short duration or laboratory simulations. Few extended studies were carried out about the effects of earthworms on the distribution of soil organisms in soil profile under field conditions, particularly far less in the upland rice-wheat rotation agro-ecosystem with corn residues manipulations. In order to confirm the relation between earthworms and soil organisms, a long-term and laboratory experiments were conducted and Metaphire guillelmis was chosen to focus on. The main objectives of these experiments are as follows:(1) Earthworm effects soil microbial population and acitivity in a long-term plot experiment; (2) earthworm effects on the functional communities of soil microorganisms and its distribution on soil profiles in a long-term plot experiment; (3) earthworm effects on the abundance and community structure of soil nematodes protozoan in a long-term plot experiment; (4) how to earthworm affects on the abundance of soil protozoa, nematode and enchytraied in a laboratory incubation experiment. The main results as follows:1 The application of corn residues (mulching and incorporation) to soil gave higher number of bacteria, fungi, actinomyces, ammonifiers, nitrogen-fixing bacteria, cellulose-decomposing microbes, inorganic phosphorus-decomposing bacteria and microbial biomass carbon (MBC) than control soil. When corn residue was mulched, the presence of earthworms had lower number of bacteria, fungi and actinomyce, and higher number of four bacterial physiological groups than the same treatment without earthworms. The presence of earthworms had higher number of bacteria, actinomyces, ammonifiers and inorganic phosphorus-decomposing bacteria in corn residue incorporation than the same treatment without earthworms. The presence of earthworms enhanced MBC in soil with corn residue mulching or incorporation. Additionally, in earthworm casts the number of bacteria, fungi, actinomyces and four bacterial physiological groups and MBC was significantly higher than those in the surrounding soil.2 BIOLOG analysis results showed that the presence of earthworms had higher microbial ability of carbon source utilization in 5-10 cm layer soil with corn residue mulching than the same treatment without earthworms and in 0-5 cm and 10-20 cm layer soil with corn residue incorporation than the same treatment without earthworm. The results of principal component analysis showed that the presence of earthworms changed carbon sources utilization by different soil microbial community at all soil depths following corn residue mulching or incorporation. In two methods of corn residue application, the presence of earthworms gave higher Shannon diversity of BIOLOG substrate utilization at all soil depths, showing a significant difference in 5-10cm layer soil with corn residue mulching. In earthworm casts, there were higher microbial ability of carbon source utilization and significantly lower Shannon diversity than those in the surrounding soil.3 The application of corn residues to soil without earthworms significantly enhanced the five soil enzyme activities compared with the control treatment during rice and wheat cultivation. The presence of earthworms further significantly enhanced protease activity in the soils with both incorporated and mulched corn residues during two cultivation seasons, but only significantly increased alkaline phosphatase activity in the soil with incorporated corn residue during the rice cultivation season. Invertase activity was significantly enhanced by the presence of earthworms in the soil with corn residue incorporation during two cultivation seasons. There were no changes in dehydrogenase activity when earthworms were present. Additionally, the five enzyme activities in earthworm casts were significant higher than those in the surrounding soil, especially dehydrogenase and invertase activities. Whatever the treatment, the values obtained for the enzyme activities in both soil and casts, except for dehydrogenase activity in earthworm casts, were significantly higher under wheat than those in rice-cultivated soil. These results indicate that the presence of earthworms strongly affected soil enzyme activities, depending on the method of organic residue application, and the enhanced enzyme activities of earthworm casts probably contributed to the surrounding soil enzyme activities.4 The addition of corn residues to soil strongly affected the abundance and community structure of nematodes and protozoa in the absence of earthworms. The presence of earthworms gave significantly lower total nematode numbers at all soil depths following corn residue incorporation than that in the same treatment without earthworms, and also gave lower (although not significantly) total nematode numbers in the upper soil layer following corn residue mulching than the same treatment without earthworms. This was mainly due to a significant decrease in bacterial-feeding nematode numbers. Earthworms also strongly affected the distribution of the number of total nematodes and two trophic groups (bacterial and plant feeders) with soil depth. In the presence of earthworms, total protozoan and flagellate numbers significantly increased at all soil depths following both incorporation and mulching of corn residues, while numbers of amoebae increased only when corn residues were mulched. Additionally, in earthworm casts total nematode numbers (mainly bacterial and fungal feeders) were significantly higher, whereas total protozoa numbers (mainly flagellates and amoebae) were significantly lower than that in soil from the 0-5cm layer. These results indicated that earthworm activity could affect the abundance and community structure of microfauna, and change their distribution between soil layers and cast material, depending on the mode of application of organic residues.5 The lmm diameter mesh would allow nematodes, enchytraeids and soluble nutrients, which developed in the inoculum soil, to migrate to the surrounding soil, while the 5μm diameter meshwould prevent the migration of nematodes and enchytraeids but still allow soluble nutrients to pass into the surrounding soil. Experimental results showed that the number of soil protozoa, nematode and enchytraeid increased with increasing of incubation time and was higher in the soil with corn residues than in the control soil. With earthworms present in inner soil of lmm and 5μm diameter mesh, the number of nematodes and enchytraeids was significantly lower than in outer soil of lmm and 5μm diameter mesh during 7 weeks; Although soil microbial biomass carbon in inner soil of lmm and 5μm diameter mesh was lower by earthworms than that in outer soil of them without earthworms, it was significantly higher than in the soil of treatment with maize residues. The presence of earthworms in inner soil of lmm diameter mesh had a higher total protozoan numbers than in outer soil of it at 7 weeks, while total protozoan numbers in inner soil of 1mm and 5μm diameter mesh were significantly higher than in outer soil of them at 3 and 7 weeks. Compared with the soil of treatment with maize residues or the outer soil of 5μm diameter mesh, the outer soil of lmm diameter mesh had a lower number of nematodes and enchytraeids. In general, the presence of earthworm affects on the number and activities of soil microorganisms in soil with corn residue; earthworm activities also changes the abundance and community structure of nematodes and protozoan, depending on the methods of corn residue application. Earthworm casts, as production of earthworm indigestion, significantly increased the number of soil microorganisms and microfaunal and enzyme activity.